1. Field of the Invention
The present invention relates to an image forming apparatus and a method thereof. More particularly, the present invention relates to a page printing type image forming apparatus and a method thereof.
2. Description of the Related Art
An ink-jet type image forming apparatus injects ink drops on a printing medium, such as paper, to form an image on the printing medium. The ink-jet type image forming apparatus is classified into line printing types and page printing types. The line printing type image forming apparatus includes a print head that injects ink drops and reciprocates the print head in a width direction of a printing medium to form an image. The page printing type image forming apparatus also includes a print head, and a plurality of nozzles are arranged in the print head that are as long as a width of the printing medium. The page printing type image forming apparatus forms images in a line of the printing medium at once while the printing medium is being conveyed.
Such an ink-jet type image forming apparatus generally includes a head chip, a plurality of nozzles and heaters to inject ink. However, the heater is easily deteriorated or an ink-injection passage is blocked because of the inferior head chip or long-time use. As a result, some of nozzles malfunction and the malfunctioning nozzle cannot properly inject ink. Therefore, an image quality of the ink-jet type image forming apparatus is seriously degraded by the malfunctioning nozzles.
A line printing type image forming apparatus can prevent degradation of image quality caused by a malfunctioning nozzle. That is, the line printing type image forming apparatus controls movement of a print head or controls a conveying speed of a printing medium to correct images distorted by the malfunctioning nozzles. However, a page printing type image forming apparatus cannot prevent degradation of image quality caused by the malfunctioning nozzles because a print head is un-movably fixed in the page printing type image forming apparatus.
FIGS. 1A and 1B show images formed by nozzles of a conventional page printing type image forming apparatus.
Referring to FIG. 1A, nozzles (NZ) of the page printing type image forming apparatus are arranged in a first nozzle line R1 and a second nozzle line R2, which are separated by a predetermined distance D in a conveying direction of a printing medium. The nozzles in the first nozzle line R1 are arranged to be deviated from the nozzles in the second nozzle line R2. Each of the nozzles is controlled to form a dot having a diameter as long as a nozzle gap I, which is a distance between two adjacent nozzles in same nozzle line. If one of the nozzles malfunctions, a white line MNL is formed as shown in FIG. 1B because the malfunctioning nozzle cannot inject ink to form dots on the printing medium. Such a white line is a critical factor in the degradation of image quality since the white line MNL is easily identified by a user.
Accordingly, a need exists for a image forming apparatus having an improved print head to substantially prevent degradation of image quality due to a malfunctioning nozzle.